Tissue calcification is an important biomarker for human disease, with microcalcifications being of paramount importance for the detection of breast cancer. Microcalcifications are of two major types. Type I crystals, found more frequently in benign ductal cysts, are birefringent and colorless, and are composed of calcium oxalate {Morgan, 2005}. Type II crystals, most often seen in proliferative lesions and associated with breast cancer cells, are composed of calcium hydroxyapatite, and are non-birefringent and basophilic {Haka, 2002}.
In the general population, breast cancer screening employs x-ray mammography {Van Ongeval, 2006}. In 30% to 50% of cases, microcalcification is the hallmark for the presence of cancer {Morgan, 2005}, although x-ray mammography cannot distinguish the chemical form of the calcium salts present, and therefore relies on the pattern of crystal deposition {Stomper, 2003}.
Mammography is currently the gold standard for the early detection of breast cancer {Bassett, 1992; Bassett 2000}. However, mammography suffers from relatively low sensitivity and specificity {Mavroforou, 2006}, and mammographic screening is limited in certain patient populations {Huo, 2002} and breast densities {Kolb, 2002}. These limitations have spurred interest in alternate modalities to detect breast cancer.